The general objective of this research is to study the role(s) of insulin and selected other hormones in the turnover of specific proteins in rat tissues. The specific purpose of the project is to study the role(s) of insulin, other hormones (e.g., cortisol, growth hormone, glucagon and thyroxine), and energy sources (e.g., glucose, fructose, and pyruvate) in the control of the turnover of glucose-6-phosphate dehydrogenase in rat adipose tissue and liver and in the control of the degradation of actin and myosin in skeletal muscle. Techniques involving the prolonged incubation of epididymal adipose tissue, the use of isolated hepatocytes, and the perfused hindquarter of rats will be used in this project in an effort to provide more rigorous control of experimental factors than is possible in the whole animal. The use of in vitro techniques in these experiments allows for the elucidation of the variables that are pertinent to the control of the turnover of these specific proteins without invoking responses from the whole-body homeostatic mechanisms.